pip无法更新到19.3.1 You are using pip version 19.2.3, however version 19.3.1 is available. You should ...

在使用pip安装sklearn包时无法下载，报错：You are using pip version 19.2.3, however version 19.3.1 is available. You should consider upgrading via the 'pip install --upgrade pip' command.

使用pip install --upgrade pip更新后提示已是最新版本19.2.3。

原因在于安装了python3后同时存在pip3，pip，而pip是在python2.7下，故更新不了19.3.1的pip

使用

pip3 install --upgrade pip

python3 -m pip install sklearn

解决